Rebound limiting device for typewriter



A ril 11, 1967 E. J. LENNEY REBOUND LIMITING DEVICE FOR TYPEWRITER 2 Sheets-Sheet 1 Filed Dec. 11, 1964 PIN SETTING AND MAINTAINING ASSEMBLY INVENTOR.

EDWIN J. LENNEY ATTORNEY.

April 11, 1967 Filed Dec. 11, 1964 DISPLACEMENT FIG. 3

E. J. LENNEY 3,313,387

REBOUND LIMITING DEVICE FOR TYPEWRITER 2 Sheets-Sheet 2 I 14 74- 1e 10 10 z 8 8 r 6 1e 6 15' 1s *2- 15; 4 g 4 l 7 2 2 O g 0 D TIME United States Patent 3,313,387 REBOUND LlP/HTTNG DEVICE FOR TYPEWRITER Edwin J. Lenney, Lexington, Ky., assignor to International Business Machines Corporation, Armonk, N.Y., a corporation of New York Fiied Dec. 11, 1964, Ser. No. 417,623 3 Ciairns. (Cl. 137-64) The present invention relates generally to the typewriter or printing arts, and more particularly to the provision of a rebound limiter or governor particularly adapted for use in a proportional encapement typewriter.

In copending application Ser. No. 311,373, filed Sept. 25, 1963, entitled, Proportional Escapement Apparatus for a Single Element Typewriter, in the names of Walter O. Cralle, In, George A. Holt, Edwin J. Lenney, Douglas E. Sederholm and Neil D. Walton, and assigned to the assignee of the present invention, there is disclosed a typewriter having highly improved proportional escapement control apparatus. The proportional escapement control apparatus comprises a pin wheel mounting a plurality of pins, each of which is movable to a set or reset state under the control of a pin setting assembly in response to character selection by the typist. The pin wheel is biased for rotation and is drivingly connected by pitch changing apparatus and a lead screw to a carrier mounting a single print element. An escapement pawl assembly is adapted to engage the set pins so that the print element and the pin wheel move by distances corresponding to the spacing between adjacent set pins on the pin wheel. During an escapement operation, the pin wheel rotates until it is abruptly stopped by the escapement pawl assembly. There is a tendency for the pin wheel and other movable portions of the escapement apparatus and printing mechanism to rebound since they have considerable inertia. It is highly desirable to limit this rebounding movement since, under certain conditions, it can cause the print element to be incorrectly positioned at the end of an escapement operation.

Briefly, this invention provides a rebound limiting or governing device of particular utility when used in connection with power driven business machines, such as electric typewriters. A rebound limiting or governing member of pedetermined mass is connected by a uni-directional clutch means to a driven member. The driven member moves in its driven direction independently of and without connection to the rebound limiting member due to the uni-directional coupling characteristics of the clutch means. The driven member moves in the driven direction with considerable inertia and is abruptly stopped. As the driven member begins to move in the rebound direction, it is immediately connected with the rebound limiting member by the uni-directional clutch means. The rebounding velocity from the driven member is dissipated in accelerating the rebound limiting member in the rebound direction and rebounding of the driven member is effectively eliminated. A brake means is provided for maintaining a slight braking force on the rebound limiting member to brake the same to a stop after it is accelerated in the rebound direction by the rebounding movement of the driven member. In the preferred embodiment of the invention, the uni-directional clutch means is a spring clutch and the brake means takes the form of a drag member which engages the rebound limiting member.

It is the primary or ultimate object of the invention to provide a rebound limiting device for very substantially reducing and effectively eliminating the rebounding movement of a driven member. The driven member is automatically connected by a uni-directional clutch with a rebound limiting member when the driven member attempts to move in the rebound direction. The rebound "ice limiting member governs and eliminates substantial rebounding movements of the driven member.

Another object of the invention is to provide a re bound limiting device of the type set forth above which is particularly useful when employed in an electric typewriter. A lead screw and a pin wheel rotates in the driven or escapement direction until this movement is abruptly halted by an escapement pawl assembly. The uni-directional characteristics of the clutch allow the movement of the lead screw and pin wheel in the escapement direction to be accomplished very quickly with a minimum of power since the rebound limiting member is not connected to the lead screw and pin wheel during this movement in the escapement direction. However, the rebound limiting member is connected to and prevents rebounding of the lead screw and pin wheel which could cause catching or final stopping of the movable apparatus in the incorrect position. v

A further object of the invention is to provide a rebound limting device having brake means to stop movement of the rebound limiting member in the rebound direction. As the driven member begins to rebound and is connected to the rebound limiting member by the unidirectional clutch, the rebound limiting member is accelerated and moves in the rebound direction. The brake serves to remove energy from the system and insures the rebound limiting member is brought to a stop before the next operational cycle of the machine occurs. While the rebound limiting device can be operated without the brake with proper selection and design of the uni-directional clutch and the rebound limiting member, its inclusion eliminates the necessity of individually selecting and adjusting the uni-directional clutches. This is important when a large number of machines are being manufactured since crititcal tolerances and adjustments are to be avoided.

A still further object of the present invention is the provision of a rebound limiting device for typewriters which is characterized by its extreme simplicity in construction and operation. The rebound limiting device comprises only a few standard mechanical elements and is ideally suited for production in large quantities at very low costs.

The foregoing and other objects and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings.

In the drawings:

FIGURE 1 is a front perspective view of escapement apparatus employed in a single element typewriter embodying a rebound limiter or governor constructed and operated in accordance with the teachings of this invention;

FIGURE 2 is a fragmentary front perspective view showing particularly the construction of the escapement pin wheel and escapement pawl assembly used in the escapement apparatus of FIGURE 1;

FIGURE 3 is a sectional view of the rebound limiting device taken generally along the section line 3-3 of FIGURE 1; and

FIGURES 4 and 5 are graphs depicting displacement of the escapement pin wheel as a function of time both when a rebound limiter is not employed and when a rebound limiter is used which are particularly useful in explaining the operation of the device.

Referring now to the drawings, and initially to FIG- URE 1 thereof, the reference numeral 10 designates generally a portion of a single element typewriter employing a rebound limiter or governor of this invention. The typewriter comprises a print element 11 detachably secured and mounted for relative movement on a carrier 12. The carrier has a driving connection, not particularly shown, with an elongated lead screw 13 extending in parallel relation with a conventional and stationarily mounted printing platen, also not shown. The amount and directions of the angular rotations imparted to the lead screw 13 determine the extent of the escapement and backspace movements of the single print element 11. The print element has the shape of a truncated spheroid and a plurality of different size characters are formed thereon in generally aligned circumferential and vertical rows. The typewriter is provided with a plurality of character keylevers and a number of function keylevers, not shown, including a case shift keylever. Each of the character keylevers is associated with two of the characters formed on the print element 11 and is operative to actuate character selection apparatus, not shown, for rotating and tilting the print element to bring one of the characters to the printing position as determined by the state of the case shift keylever.

The escapement apparatus for the typewriter comprises lead screw 13 and means for rotating the lead screw in the proper direction and through preselected angular distances corresponding to the escapement distances associated with selected characters. A constant torque drive device is connected to one end of the lead screw 13 and exerts a constant driving torque which turns the lead screw as indicated by arrow 14 and controls the carrier 12 and print element 11 to advance longitudinally from left to right in the character spacing direction15 in front of the stationary printing platen during an escapement operation. This constant torque device is represented schematically by reference number 24 in FIGURE 1 of the drawings and preferably is of the type disclosed in copending patent application Ser. No. 311,376 entitled Constant Torque Drive Means for Typewriter, filed Sept. 25, 1963, and assigned to the assignee of this invention.

Movement of carrier and print element in the character spacing direction 15 is limited by escapement control apparatus 16 comprising a pin wheel 17 carrying a plurality of pins 18 and an escapement pawl assembly 19, the latter being shown in FIGURE 2 of the drawings. The pin wheel 17 is biased for rotation by the constant torque drive device 24 in the direction indicated by arrow 14. Pitch changing apparatus 26) provides a variable drive connection between the escapement control apparatus 16 and the lead screw. Backspacing apparatus, not shown, is provided for driving the escapement pin wheel 17 in a direction which causes the lead screw 13 to rotate and advance the carrier 12 and print element 11 back toward the left end of the stationary printing platen in the backspacing direction. A rebound limiter or governor 21, to be hereinafter more fully described, is provided at the other end of the lead screw 13 to limit undesired rebounding of the movable apparatus during escapement operations which could result in incorrect positioning of the carrier and print element.

The escapement control apparatus 16 is best shown in FIGURE 2 of the drawings and comprises the pin wheel 17 keyed to a shaft 22. The pin wheel has a plurality of axially extending and equally spaced slots formed therein for receiving the pins 18. Each of the pins 18 has a length longer than the axial thickness of the pin wheel 17 and is settable in either of two states. The first or set state for a pin 18 is when the end thereof projects outwardly from the left side of the pin wheel when looking at FIG- URE 2 of the drawings. A pin is in its other or reset state when a portion of the pin extends outwardly from the right side of the pin wheel. A garter spring 23 extends about the periphery of the pin wheel 17 and, in combination with recesses in the upper edges of the pins 18, defines a detent means for holding and maintaining the pins in their set and reset states. The distance between two of the pins 18 defines a standard or basic single escapement unit.

The escapement pawl assembly 19 includes an escapement pawl 25 having an elongated aperture 26 therein which serves to mount the escapement pawl for pivotal and limited longitudinal movement on pivot pin 27. The escapement pawl 25 is positioned to one side of the pin wheel 17 in such a manner that the tip portion thereof is adapted to engage only the ends of the set pins which project outwardly from the left side of the pin wheel. The escapement pawl is normally biased into engagement with the set pins by a tension spring 28. Also mounted for pivoting movement on the pivot pin 27 in aligned sideby-side relation with respect to the escapement pawl 25 is a holding pawl 30 having a tip portion which is adapted to engage each one of the pins 18 regardless of the state thereof. This is accomplished by providing a slot 31 along one side of the pin wheel and it should be noted that a portion of each of pin 18 is always within this slot.

During an escapement operation, a pulling force is applied to one end of an escapement pawl trip lever 32 which is pivoted on the pin 27. The transversely extending end portion of the escapement pawl trip lever 32 first engages the rear end of the holding pawl 30 and lifts the tip portion thereof from engagement with the pins 18. The pin wheel is still hold at this time since the tip portion of the escapement pawl 25 still engages one of the set pins 18. Eventually, after the holding pawl 30 has been retracted, the end portion of the escapement pawl trip lever 32 bears against the rear end of the escapement pawl 25. The escapement and holding pawls 25 and 30 then pivot in a counterclockwise direction as a unit and the tip portion of the escapement pawl 25 is removed from engagement with the set pin 18. The spring 28 immediately moves the escapement pawl forward due to the elongated aperture 26 therein and a depending tab 33 on the escapement pawl 25 moves over on an extension 34 carried by the holding pawl 30. The tab 33 and the extension 34 define a latch which maintains the tip portion of the holding pawl 30 in elevated relation with respect to the tip of the escapement pawl 25 and prevents the holding pawl from dropping down and engaging a pin before the escapement pawl has returned to its original position.

The spring 28 not only moves the escapement pawl 25 forwardly but also pivots the tip portion thereof back into engagement with the set pins 18 carried by the pin wheel 17. The next adjacent set pin 18 in the direction of rotation of the .pin wheel engages the tip portion of the escapement pawl 25 and return this member to its original position. The tab 33 moves from the extension 34 and the holding pawl 39 drops down behind the set pin 18 engaged by the escapement pawl. The holding pawl 30 is necessary during backspacing operations since the escapement pawl 25 cannot accurately hold the pin wheel 17 against rotation in the backspace direction due to the elongated aperture 26 therein and the fact that the escapement pawl is positioned to engage only those of the pins which are in the set state. The backspacing apparatus, not shown, is operative to rotate the pin wheel 17 in the backspace direction against the force exerted by the constant torque drive device by incremental distances slightly greater than the spacing between two adjacent pins 18. The arrangement is such that the holding pawl 30 overrides and drops down behind the next adjacent pin 18 in the backspace direction to hold the pin wheel and the rest of the escapement apparatus in their new positions. The incremental backspacing operations are repeated either under manual control or automatically until the print element is moved in the backspace direction sufi'iciently to be positioned at the selected previous printing position.

Positioned directly in front of the escapement pawl assembly 19 is a pin setting mechanism, shown schematically at 31 in FIGURE 2 of the drawings, which is responsive to character escapement selection apparatus when the typist selects a character. The pin setting assembly is operative to position the pins 18 to define angular distances through which the pin wheel 17 is allowed to rotate during an escapement operation in accordance with the characters selected. The distances through which the pin wheel 17, lead screw 13, carrier 12 and print element 11 move during an escapement operation are dependent on the number of reset pins between adjacent set pins on the pin wheel. The pin setting mechanism determines this relationship in accordance with the character selected. For example, in one constructed embodiment of a single element typewriter, three basic escapement units are associated with a character of small width, such as the lower case i, while nine units are associated with a character of large width, like the upper case M or W.

The pitch changing apparatus 20 is disposed between the lead screw 13 and the pin wheel 17 to provide an adjustable gearing means for regulating the distance travelled by carrier 12 and interchangeable print element 11 for each basic escapement unit. While the escapement control apparatus 16 defines the absolute number of basic escapement units associated with an escapement operation, the pitch changing apparatus 20, under typist control determines the actual distance moved by the carrier 12 and print element 11. This apparatus provides the typist with a means for changing the pitch or the average number of characters printed in a predetermined length to vary the appearance of material printed with the same print element or to allow the printing of material with various size type styles formed on different print elements.

As shown in FIGURE 1 of the drawings, the shaft 22 mounting the pin wheel 17 extends through a side plate of a bracket 37. Keyed or otherwise rigidly attached to the projecting end of the shaft 22 in aligned side-by-side relation are three pinion gears 4tl42 each having the same number of teeth and, as a consequence, different pitches (the number of teeth per unit distance of pitch circumference). Meshing with the pinion gears 40-42 are pitch gears 43-45 each having the same pitch as the corresponing one of the pinion gears 49-42. The pitch gears 43-45 are mounted for independent rotary movement on shaft 46 which is disposed in parallel relation with respect to shaft 22 and extends between the side plate of bracket 37 and a spaced frame 47. Means are provided for detachably securing any selected one of the pitch gears 43- 45 in driving engagement with the shaft 46. The pitch gears 43-45, in combination with the pinion gears 40 12, define three selectable gear sets each capable of drivingly interconnecting the shafts 22 and 46. The shaft 22 mounts the pin wheel 17 while the shaft 46 is connected by a gear train comprising gears 49-51 to lead screw 13.

The selected one of the gear sets 40, 43; 41, 44 or 42, 45 which drivingly interconnects the shafts 22 and 46 determines the extent of actual movement of the carrier 12 and print element 11 for each basic escapement unit. For example, when the gear set comprising gears 42 and 45 is selected, the lead screw 13 will rotate a greater angular distance for a predetermined angular movement of the pin wheel 17 than if either of the other gear sets has been selected under the same condition. Similarly, if the gear set comprising gears 41 and 44 is selected, the carrier and print element move through a greater distance for the predetermined angular movement of pin wheel 17 than when the gear set including gears 40 and 43 operatively interconnects the shaft 22 and 46.

All of the apparatus with the specific exception of the rebound limiter or governor 21, is shown and described in the above mentioned co-pending application Ser. No. 311,373. In addition, other information concerning various portions of the typewriter is contained in copending patent applications Ser. Nos. 311,377 and 311,375 entitled Pitch Changing Apparatus for Proportional Escapement Typewriter and Backspacing Apparatus for Proportional Escapement Typewriter, and respectively, both filed Sept. 25, 1963, and assigned to the assignee of the present invention. The basic single element typewriter is of the type manufactured and sold by International Business Machines Corporation, Armonk, N.Y., as set forth in the 6 IBM Customer Engineering Series 72 Instruction Manual Form 241-5032-0, copyright 1961.

The rebounding limiting device 21, as shown in FIG- URES 1 and 3 of the drawings, comprises an annular inner hub 60 which is rigidly attached to lead screw 13 by means of set screw 61. Spaced from the inner hub 60 and loosely received over the outer end of the lead screw 13 is an outer hub 62 which carries an annular rebound limiting member 63. Spanning and received over the inner and outer hubs 60 and 62 is a spring clutch 64 whose inner end 65 is staked to the inner hub 69. The spring clutch 64 is wound in such a direction that when the lead screw 13 is turned in the escapement or driven direction as represented by arrow 14, the convolutions thereof are subjected to unwinding forces. The rebounding limiting member 63 is efiectively disconnected from the lead screw 13 and other movable portions of the escapement apparatus. However, movement of the lead screw 13 in the backspace or rebound direction immediately results in tightening of the spring clutch 64 about outer hub 62 so that the lead screw 13 and rebound limiting member 63 are connected and move together.

A brake is incorporated to quickly bring the rebound limiting member 63 to a stop after it has been accelerated or moved in the rebound direction when the movable portions of the escapement apparatus tend to move in the rebound or backspace direction. This brake comprises a generall U-shaped drag member 66 formed from strip steel which extends from stationary stud 67. The arms 68 of the drag member 66 have formed outer end portions which mount brake linings 69 of cork or other similar material that engage the rebound limiting member 63 on the opposite sides thereof. The braking force is controlled by adjustment of bolt and nut assembly 70 extending between the spaced arms 68 :of drag member 66. The braking force is small and is adjusted so that it is just sufiicient to bring rebound limiting member 63 to a stop before the time at which the next escapement operation can occur.

While the brake is preferred in most instances, considerable success has been had in operating the rebound limiting device 21 without the brake. A small rotation of the rebound limiting member 63 in the escapement direction reduces the effective backlash of the spring clutch 64. The rebound limiting member 63 will turn very little in the rebound direction without a brake if the inertia of the rebound limiting member 63 and the drag characteristics of the spring clutch are correctly selected. The brake, while not interfering with normal escapement operations, allows more latitude in the design and adjustment of the various parts and would normally be employed when a large number of machines are to be manufactured and it is desired to avoid relatively critical adjustments.

Considering now the operation of the rebound limiting device 21 described above, it will be assumed the escapement apparatus is at rest with the escapement and holding pawls 25 and 30 engaging one of the set pins 18 on pin wheel 17 and preventing rotation of the lead screw 13 and pin wheel. The typist depresses a character keylever and the pin setting mechanism is actuated to determine the states of the pins directly in front of the printed, a pulling force applied to escapement pawl printed, a pulling force applied to escapement pawl lever 32 removes the escapement and holding pawls 25 and 30 from engagement with the set pin 18 as fully described in previous portions of this specfication. The lead screw 13, the operative pitch gear set and the pin wheel 17 now rotate very quickly in the escapement direction under the action of the constant torque device to control movement of the carrier 11 and print element 11 in the character spacing or escapement direction. The rebound limiting device 11 is ineffective at this time since the rotation of the lead screw 13 tends to unwind 7 the turns of spring clutch 64 and the rebound limiting member 63 is disconnected from the escapement apparatus. The lead screw, the operative pitch gear set and pin wheel build up considerable speed and momentum as they move in the escapement direction.

Eventually, the next set pin 18 on the pin wheel 17 in the escapement direction engages the tip portion of the escapement pawl 15 and returns the escapement pawl assembly to its original condition. The pin wheel 17, the lead screw 13 and all other moving portions of the escapement apparatus are subjected to a very sudden stopping force. These portions tend to rebound or rotate in the backspace direction and the turns of the spring clutch 64 are tightened to effectively connect the lead screw 13 with the rebounding limiting member 63. The rebounding momentum is dissipated in accelerating and moving the rebound limiting member 63 and rebounding of the movable portions of the escapement assembly is effectively eliminated.

The use and advantages of the rebound limiting device 21 are clearly demonstrated in the graphs of FIG- URES 4 and of the drawings. These graphs were obtained by attaching a displacement potentiometer on the end of an escapement pin wheel and observing resulting displacement-time curves occurring during an escapement operation on an oscilloscope. FIGURE 4 depicts a curve observed over an escapement distance of ten basic escapement units each approximately 0.1 inches in length when a rebound limiting device 21 was not employed. When the escapement operation is tripped at oint 72, the pin wheel and all of the other movable parts of the escapement apparatus accelerate and move at a high speed as represented by the curve portion 73. Each horizontal division on the scale of the graph represents milliseconds. The next adjacent set pin encounters the escapement pawl and an abrupt stopping force is applied to the moving portions of the esca ement system. There is a tendency for these portions to continue moving in the same direction against the stopping force and a slight overtravel occurs due to deflections in the system as represented by curve portion 74. Then the moving portions rebound in the backspace direction as a reaction to the abrupt stopping force along curve portion 75. The amount of rebound in this instance is so great the pin wheel moves more than one basic escapement unit in the backspace direction. This allows the holding pawl to drop behind the next and unset pin on the pin wheel in the backspace direction. The system then comes to rest as represented by curve portion 76. The print element is incorrectly positioned since it has moved through an effective escapement distance corresponding to nine basic units of escapement even though ten basic escapement units were indicated by the setting of the pins on the pin wheel due to the rebounding of the movable portions of the escapement apparatus.

This fault condition is eliminated when the rebound limiting device of the present invention is employed as shown by the curve of FIGURE 5 of the drawings. The vertical and horizontal, scales of this graph are the same as those set forth above the graph shown in FIGURE 4 of the drawings. Portions of the curve in this figure are designated by primed numerals of the same value as those used in designating the portions of the curve shown in FIGURE 4 of the drawings. When the moving portions of the system are subjected to the abrupt stopping force due to the escapement pawl engaging the tenth and set pin on the pin wheel, the rebound limiting member is connected by the spring clutch with the lead screw and rebounding, as represented by curve portion 75' is limited to a very small displacement approximating the rotation required to tighten the spring clutch about the outer hub and is effectively eliminated. The print element is correctly positioned in accordance with the escapement distance selected as required.

Best results have been obtained in effectively eliminating rebounding when the rebound limiting member is designed to have an inertia approximately equal to or slightly greater than the inertias of the movable parts of the escapement system, including the pin wheel, one pitch changing gear set and the lead screw. If the inertia of the rebound limiting member 63 exactly equals the inertia of the movable portions of the escapement system and friction forces are ignored, the movable portions of the escapement system will have zero velocity while the rebound limiting member 63 will move in the rebound direction with a certain velocity immediately after the spring clutch 64 has been tightened. Alternately, if the inertia of the rebound limiting member 63 is greater than that of the movable portions of the escapement system, the rebound limiting member will move in the rebound or backspace direction with a certain velocity and the movable portions of the escapement apparatus will move in the escapement direction with another velocity. Under the latter condition, the pin wheel tends to rebound, is connected with the rebound limiting member and then moves forward again toward the escapement pawl assembly where it comes to rest.

The use of the uni-directional clutch means is important in that the rebound limiting member is disconnected from the movable portions of the escapement apparatus and does not alter in any appreciable manner their operations or the power required to drive the same during normal escapement operations. it is recognized the rebound limiting member is connected to the lead screw during backspacing operations but considerable power is available for rotating the pin wheel in the backspace direction and this rotation takes place at a reduced rate of speed compared to the movement of the pin wheel during an escapement operation. It should be apparent that uni-directional clutches other than spring clutches can be employed with the rebound limiting devices of this invention.

The rebound limiter could be successfully located at any of a number of places in the escapement system, such as the end of shaft 22 mounting the pin wheel or the end of shaft 46 carrying the pitch gears 4345. In this connection, the terminology coupled to or coupling employed in the claims is intended to cover not only a direct connection between two members, but also a connection which includes intermediate drive connections, such as gears and shafts, for example. The location at the end of the lead screw is preferred, however, because the lead screw rotates at a faster rate than the other parts. Thus, any movement required by the lead screw 13 in the backspace direction before the turns of the clutch spring tighten sulficiently to connect the rebound limiting member with the system are reflected back through the gears of the pitch changing apparatus and result in much less rotational movement of the pin wheel. This is desirable since any rebounding of the pin wheel by a distance greater than a single basic escapement unit as defined by the distance between two of the pins is unacceptable and must be avoided.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A rebound limiting device for substantially eliminating the rebound in a typewriter escapement system comprising:

a typewriter carrier adapted to be moved in a stepwise manner in an escapement direction to a plurality of escapement positions;

an elongated lead screw coupled to said carrier;

drive means coupled to said lead screw tending to rotate the same in a first direction which controls the movement of said carrier in said escapement direction;

a generally disc shaped pin wheel carrying a plurality of pins;

means drivingly interconnecting said lead screw and said pin wheel whereby said pin wheel is biased for rotation by said drive means;

each of said pins being movable to at least two positions defining at least two states and the distance between two adjacent pins defining a basic escapement unit;

means for setting and maintaining said pins in selected states in accordance with selected characters;

an escapement assembly comprising a first removable escapement member engaging those of said pins in one of said states to cause said pin wheel and lead screw to stop at positions defined by said pins in said one of said states and a second removable escapement member positioned to engage all of said pins regardless of the states thereof;

means to remove said first and second escapement members from said pin wheel and position said first escapement member in a position to be engaged by a pin in said one of said states;

a rotatable disc shaped rebound limiting member located adjacent said lead screw; and

a uni-directional clutch means coupling said rotatable rebound limiting member for movement with said lead screw only when said lead screw rotate in a second direction in reaction to a pin in said one of said states on said pin wheel engaging said first escapement member to stop rotation of said pin wheel and lead screw at the escapement position defined by said pin. 2. Apparatus according to claim 1 further characterized by:

a brake means continuously engaging said disc shaped rebound limiting member to brake movement thereof. 3. Apparatus according to claim 2 further characterized by:

References flited by the Examiner UNITED STATES PATENTS 9/ 1911 Barrett.

2/1951 Stinson 197-434 X 4/1952 Serednicky et al. 192-12 12/ 1957 Sagner 19764 12/1965 Cetran et al. 197-84 References Cited by the Applicant UNITED STATES PATENTS 8/1956 McFadden. 2,864,260 12/1958 Nicolaus.

ROBERT E. PULFREY, Primary Examiner.

E. T. WRIGHT, Assistant Examiner. 

1. A REBOUND LIMITING DEVICE FOR SUBSTANTIALLY ELIMINATING THE REBOUND IN A TYPEWRITER ESCAPEMENT SYSTEM COMPRISING: A TYPEWRITER CARRIER ADAPTED TO BE MOVED IN A STEPWISE MANNER IN AN ESCAPEMENT DIRECTION TO A PLURALITY OF ESCAPEMENT POSITIONS; AN ELONGATED LEAD SCREW COUPLED TO SAID CARRIER; DRIVE MEANS COUPLED TO SAID LEAD SCREW TENDING TO ROTATE THE SAME IN A FIRST DIRECTION WHICH CONTROLS THE MOVEMENT OF SAID CARRIER IN SAID ESCAPEMENT DIRECTION; A GENERALLY DISC SHAPED PIN WHEEL CARRYING A PLURALITY OF PINS; MEANS DRIVINGLY INTERCONNECTING SAID LEAD SCREW AND SAID PIN WHEEL WHEREBY SAID PIN WHEEL IS BIASED FOR ROTATION BY SAID DRIVE MEANS; EACH OF SAID PINS BEING MOVABLE TO AT LEAST TWO POSITIONS DEFINING AT LEAST TWO STATES AND THE DISTANCE BETWEEN TWO ADJACENT PINS DEFINING A BASIC ESCAPEMENT UNIT; MEANS FOR SETTING AND MAINTAINING SAID PINS IN SELECTED STATES IN ACCORDANCE WITH SELECTED CHARACTERS; AN ESCAPEMENT ASSEMBLY COMPRISING A FIRST REMOVABLE ESCAPEMENT MEMBER ENGAGING THOSE OF SAID PINS IN ONE OF SAID STATES TO CAUSE SAID PIN WHEEL AND LEAD SCREW TO STOP AT POSITIONS DEFINED BY SAID PINS IN SAID ONE OF SAID STATES AND A SECOND REMOVABLE ESCAPEMENT MEMBER POSITIONED TO ENGAGE ALL OF SAID PINS REGARDLESS OF THE STATES THEREOF; MEANS TO REMOVE SAID FIRST AND SECOND ESCAPEMENT MEMBERS FROM SAID PIN WHEEL AND POSITION SAID FIRST ESCAPEMENT MEMBER IN A POSITION TO BE ENGAGED BY A PIN IN SAID ONE OF SAID STATES; A ROTATABLE DISC SHAPED REBOUND LIMITING MEMBER LOCATED ADJACENT SAID LEAD SCREW; AND A UNI-DIRECTIONAL CLUTCH MEANS COUPLING SAID ROTATABLE REBOUND LIMITING MEMBER FOR MOVEMENT WITH SAID LEAD SCREW ONLY WHEN SAID LEAD SCREW ROTATE IN A SECOND DIRECTION IN REACTION TO A PIN IN SAID ONE OF SAID STATES ON SAID PIN WHEEL ENGAGING SAID FIRST ESCAPEMENT MEMBER TO STOP ROTATION OF SAID PIN WHEEL AND LEAD SCREW AT THE ESCAPEMENT POSITION DEFINED BY SAID PIN. 